1. Field of the Invention
This invention relates, generally, to squeeze film dampers for controlling rotor vibrations and, more particularly, to an improved squeeze film damper the damping coefficient of which remains substantially constant over the full range of rotor vibratory displacement.
2. Description of the Prior Art
In high speed rotor applications, such as gasifier rotors in gas turbine engines, dynamic unbalance generates vibrations during rotor rotation which are commonly controlled or damped by squeeze film type dampers. In typical, plain squeeze film dampers where oil filled annuli are formed between stationary plain cylindrical surfaces and plain cylindrical surfaces vibrating with the rotors, coefficients of damping are relatively constant for vibratory radial displacements up to about 50% of the available clearance or depth of the squeeze film annuli. Beyond 50% displacement, the coefficients of damping in plain dampers become non-linear and the dampers become objectionably stiff. Thus, as a practical matter, 50% of the available clearance in plain squeeze film dampers is unproductive in the sense of providing damping and counterproductive in the sense that corresponding clearances are required within the engine between the rotor and surrounding stationary components such as seals. To minimize internal engine clearances, some plain dampers incorporate springs which center the rotor when the latter is stopped or rotating below damper lift-off speed and some plain dampers are teamed with external snubbers which physically limit the amount of radial displacement of the rotor. These proposals, however, are complex, expensive, and consume valuable space in the engine. A squeeze film damper according to this invention represents an improvement over these and other known plain squeeze film dampers and exhibits a substantially linear or constant damping coefficient characteristic for vibratory radial displacement of the rotor up to substantially the entire available clearance.